Method of fastening a tab to a metallic container wall



Oct. 17, 1967 G. J. HENNING ETAL 3,346,948

METHOD OF FASTENING A TAB TO A METALLIC CONTAINER WALL 7 Sheets-Sheet 1 Filed Aug. 14, 1964 G INVENTORS ear eeliiemw'ug BY amzzdgseph Scwbiw ATTORNEYS WALL Oct. 17, 1967 G.J.HE.NN1NG ETAL METHOD OF FASTENING A TAB TO A METALLIC CONTAINER 7 Sheets-Sheet 2 Filed Aug. 14, 1964 Ge m INVENTORS or e elliazmi elgsqph Saw BY Mb QQW ATTORNEYS Oct 17, 1967 G. J. HENNING ETAL 3,346,948

METHOD OF FASTENING A TAB TO A METALLIC CONTAINER WALL Filed Aug. 14, 1964 v Sheets-Sheet F? INVENTORS Gear eeZHe 621ml sepia Sam/L I? ATTORNEYS Oct. 17, 1967 G. J. HENNING ETAL 3,346,948

METHOD OF FASTENING A TAB TO A METALLIC CONTAINER WALL Filed Aug. 14, 1964 '7 Sheets-Sheet 4 INVENTORS' 661:}:9'8 U Hen/Jug BY and 08633216 Sawlzm Q WWQ2 W ATTORNEYS Oct. 17, 1967 G. J- HENNING ETAL 3,346,948

METHOD OF FASTENING A TAB TO A METALLIC CONTAINER WALL Filed Aug. 14. 1964 7 Sheets-Sheet 5 INVENTORS G801 e e]. Henna BY m hsm y 9 W 8! M46 ATTORNEYS 196? G. J- HENNlNG ETAL 3,346,948

METHOD OF FASTENING A TAB TO A METALLIC CONTAINER WALL '7 Sheets-Sheet '7 Filed Aug. 14, 1964 ATTORNEYS United States Patent 3,346,948 METHOD OF FASTENING A TAB TO A METALLIC CONTAINER WALL George J. Henning, Canton, and Joseph Scalia, Massillon, Ohio, assignors to The Central States Can Corporation, Massillon, Ohio, a corporation of Ohio Filed Aug. 14, 1964, Ser. No. 389,573 5 Claims. (Cl. 29509) ABSTRACT OF THE DISCLOSURE A procedure for connecting a pull tab to the end of a tear strip in a metal container wall wherein successively smaller bubble shapes are formed in the metal wall initially from the wall metal and then from the preceding bubble shape by drawing operations; thinning the metal in the crown of the bubble during successive drawing op erations; then reforming the bubble to cup-shape with a cylindrical cup side wall and an end wall of the same thickness as the crown thickness of the last formed bubble shape; telescoping a hole in a pull tab over the cup shape; then upset riveting the cup shape to form a rim engaging the pulltab by outward downward folding of the cup side wall without thinning the cup end wall while internally supporting the cup side wall portion remote from the end wall.

Our invention relates to improvements in container manufacture and more specifically to containers having tear strips formed in the end closures thereof. Even more specifically, our invention relates to the method of forming metal container closures of the type having a tear strip formed in the closure central wall portion and a tear strip tab secured to the closure tear strip which may be grasped for initiating and completing the tearing of the tear strip.

Various forms of tear strips for container closures have been provided arranged for use by the consumer to re move a part or all of the container end closure in order to gain access to the contents of the container. One form of these is of the type in which the end closure is secured over the open end of the container completely around the closure periphery and the tear strip is formed inwardly of this closure edge portion so that all or a portion of the closure central wall portion is removed upon manipulation of the tear strip, while the fastened peripheral edge 7 portion of the closure remains with the container body.

In this form of closure tear strip in which the tear strip is located in the closure central wall portion, it has been a problem as to just how to initiate the tearing of the tear strip and to further complete the tearing thereof, which tearing might extend over a relatively large area of the closure central wall portion. The most practical means found for accomplishing this tearing action is to provide a separate tear strip tab overlying the closure central wall portion and secured to this wall portion at the initial part of the tear strip so that the tab may be grasped and urged upwardly to initiate the tearing action, and may then be used to complete the entire desired tearing of the tear strip.

This, however, presents a major problem as to just how to secure the tear strip tab to the closure central wall portion in such a manner that the tab will not break free of the tear strip during the initiating and completion of the tearing action. This is a particularly critical problem when it is considered that the metal thickness used for forming these container closures is usually in the order of 0.010 inch metal thickness so that little metal thinning might be tolerated if the final container is to remain airtight, and even more critically, if it is to contain internal pressures or vacuum such as is encountered with various forms of contained beverages and hot packed foods.

One means proposed for the fastening of the tear strip tab to the thin metal closure central wall portion has been by the use of various forms of welding. This fastening method has proved to be unsatisfactory for the reason that it is virtually impossible to provide a sufficiently strong welded bond between the tab and closure wall portion for withstanding the necessary metal tearing forces due to the thinness of the closure wall metal and particularly without puncturing the closure wall portion.

Various forms of the modern metal-to-metal adhesives have also been attempted for accomplishing this tab fastening operation, all of which, to date, have proven to be unsatisfactory due to the lack of the necessary bonding strength for withstanding the relatively high metal tearing forces required.

Still further attempts have been made to fasten tear strip tabs to closure wall portions by the simple means of providing separate metal rivets fastened completely through both the tab and closure wall portion. Here again, these attempts have proven completely unsatisfactory due to the fact that it is impossible to properly seal such a rivet against both the closure wall portion and tab, and against the openings necessarily required therethrough, in order to provide a final airtight sealed container which will withstand either the pressures or vacuum as hereinbefore discussed.

Thus it has been found that the only practical means for securing these tear strip tabs to the closure wall portions is by the formation of an integral upstanding rivetlike member directly from the closure wall portion, passing this rivet-like member through a pre-planned opening in the tear strip tab, and then upsetting the rivet-like member so as to provide a rim portion overlying the tab and securing the tab to the closure wall portion. This solution to the problem has, however, presented considerable problems again due to the fact that the metal forming the closure wall portion is extremely thin and the rivet-like member must not only first be formed in a relatively deep drawing die operation, but after this initial formation, must have suflicient wall thickness and strength to withstand the upsetting operation for finally securing the tab to the wall portion.

One such method previously proposed for the formation of these integral rivet-like members in the thin closure wall portions has been by the use of certain die operations for crowding or drawing metal from the closure wall portion outwardly of the area of the final rivet-like member into this area, in an attempt to provide a final rivetlike member of a wall thickness increased over the thickness of the original closure wall portion. During this attempted thickening of the metal in the rivet-like member, it is particularly attempted to more greatly increase the metal thickness in the end wall of the rivet-like member, which end wall in this particular method must ultimately form the final overlying rim portion serving as the securing means between the tab and closure wall portion.

Thus, in this prior method, the rivet-like member is formed of a side wall height extending above the closure wall portion merely sufliciently greater than the thickness of the tear strip tab so that the end wall will lie slightly above the upper surface of the tab. Then, in the upsetting or overlying rim forming operation, by fully internally supporting the rivet-like member and particularly the end wall thereof, an impact force is applied downwardly against the rivet end wall, causing this end wall to thin in the central portions thereof and the metal of this end wall outwardly in all directions for making up the increased area of the rivet rim overlying and securing the tab to the closure wall portion.

To state it in simple terms, this prior method requires the formation of the rivet-like member integral in the closure wall portion having the end wall of this rivet of thickened metal, much greater thickness than the original metal thickness of the closure wall portion, and then depending on this increased rivet end wall thickness to supply sufiicient metal so that an impact force against the rivet end wall, while this end wall is fully supported, will cause the end wall to thin and a large portion of the metal thereof to flow outwardly in all directions so as to provide the increased metal area necessary for the formation of the final tab fastening rivet rim portion. Furthermore, this final integral fastening rivet must not only have sufficient final metal thickness and strength in the end wall upset or rim portion thereof, but also in the side walls thereof, in order to withstand the relatively high forces necessarily exerted during the closure tearing opera tion, and also sufiicient thickness and strength to withstand and maintain the container sealed, particularly against internal pressures or vacuum.

One of the principal difiiculties with this prior integral rivet method and construction is that the intricate die operations for accomplishing the rivet metal thickening and subsequent impact metal thinning require extremely close manufacturing control. For instance, using a given set of dies, slight variations in the thickness of the original metal from which the closure is formed can result in either improper tab fastening or an excessive thinning of the rivet end wall during the upsetting or rim forming operation, thereby resulting in a relatively high incidence of improperly formed or scrap closures.

Furthermore, relatvely slight variations in metal hardening can cause metal tearing during the formation of the rivet-like member as well as during the rivet upsetting or rim forming operation, again causing a relatively high incidence of punctured and therefore unusable closures. Also, such metal hardness variation can again result in either improper tab fastening or excessive rivet metal thinning, particularly in the rivet end wall during the impact rivet rim forming operation.

Itis, therefore, a general object of the present invention to provide methods for securing tear strip tabs to closure end walls by means of closure integral rivet-like members which overcomes the difficulties and disadvantages of the prior methods as discussed in the foregoing.

It is a primary object of the present invention to provide methods for securing tear strip tabs to closure end walls by means of closure integral rivet-like members in which impact forces and metal thinning is not required in final tab fastening operation.

It is a further object of the present invention to provide methods for securing tear strip tabs to closure end walls by means of closure integral rivet-like members in which the closure wall metal is slightly thinned over a relatively wide area in the location of the final rivet-like member during the early stages of formation of such rivet-like member, but after this initial slight thinning, during the final stages of formation of the rivet-like memher and during the tab securing upsetting or rim formation thereof, the metal thickness is merely repositioned without further thinning.

It 'is still a further object of the present invention to provide methods for securing tear strip tabs to closure end walls by means of closure integral rivet-like members in which the integral rivet-like member is formed by a series of gradual die steps resulting in a final rivet-like member of uniformly relatively thick side and end walls, even after the final tab fastening rim forming operation.

It is an additonal object of the present invention to pro vide methods for securing tear strip tabs to closure end walls by means of closure integral rivet-like members in which, although a series of relatively intricate die operations are required, such die operations are not highly sensitive to reasonable and usual metal thickness and hardness variations, so that strong and satisfactory tab fastening may be accomplished under usual production conditions and working tolerances.

without encountering unusual or excessive scrap rates over 1 those normally encountered in the container industry.

Finally, it is an object of the present invention to provide methods for securing tear strip tabs to closure end walls by means of closure integral rivet-like members which satisfy the above objects in a relatively simple and efficient manner, and whereby tear strip closures for containers may be supplied at a minimum of cost.

These and other objects are accomplished by the math ods, procedures, and forming and assembly steps comprising the present invention, preferred embodiments of which, along with apparatus and formed parts-illustrative of the best modes in which applicants have contemplated applying the principles-are set forth in the following description and illustrated in the accompanying drawings, and which are particularly and distinctly pointed out and set forth in the appended claims forming a part hereof.

In general terms, the methods for securing tear strip tabs to metal closure end walls by means of closure integral rivet-like members may be stated as including the general procedure of forming the rivet-like member spaced inwardly of the closure edge portionfrom the metal of the closure end wall portion in a series of progressively smaller diameter stages, with the closure metal wall thickness being slightly thinned in the initial stages to gain the increased metal area required for the final rivet shape, and then merely repositioning this slightly thinned end wall to finally form the rivet, as well as provide the rivet with a rim portion overhanging the tear strip tab.

More specifically, the methods of the present invention may include the steps of forming a first integral upstanding semispherical-like bubble in the closure end wall portion of a maximum diameter larger than the final rivet and with slight thinning of the metal within said bubble and in a surrounding area extending slightly outward of said bubble; then forming the first bubble into successive intermediate and second semi-spherical-like bubbles, each preferably totally from the metal Within the preceding,

bubbles, and with each having maximum diameters less than said preceding bubbles but still larger than the final rivet and with slight further thinning of the metal forming said first bubble; then forming the second bubble into the final generally hollow cylindrical upstanding rivet having a hollow cylindrical side wall and transverse end wall spaced above the closure end wall portion, said final rivet having a maximum diameter less than the maximum diameter of said second bubble, and while merely repositioning the metal of said second bubble without apprecia'bly changing the metal thickness; then positioning the tear strip tab flatwise over the surface of the closure end Wall portion with said final rivet extending through a hole in said tab and with the rivet end wall spaced above the upper tab surface; and finally repositioning the rivet transverse end wall axially downwardly and collapsing an upper part of the rivet side wall downwardly and outwardly so that said collapsed portion of the rivet side wall partially overlies the tab ground the tab hole, such repositioning and collapsing being accomplished without impacting and without further thinning of the metal forming said rivet.

By way of example, illustrative die constructions, the various stage closure parts formed by such die constructions, and the various procedural steps of the methods of the present inventionare illustrated in the accompanying drawings forming a part hereof, wherein like numerals indicate similar parts throughout the several views, and in which:

FIG. 1 is a vertical sectional view of the first stage bubble closure part;

FIG. 2, an enlarged fragmentary vertical section of the first stage bubble dies;

FIG. 3, a view similar to FIG. 1 of the intermediate stage bubble closure part.

FIG. 4, a view similar to FIG. 2 of the intermediate and second stage bubble die prior to the complete operation of the intermediate stage;

FIG. 5, a view similar to FIG. 4 of the intermediate and second stage bubble die after operation of the intermediate stage for forming the intermediate stage bubble closure part of FIG. 3;

FIG. 6, a view similar to FIG. 1 showing the second stage bubble closure part;

FIG. 7, a view similar to FIG. 4 showing the intermediate and second stage bubble die after operation of the second stage;

FIG. 8, a view similar to FIG. 1 showing the final rivet stage closure part;

FIG. 9, a view similar to FIG. 2 showing the final rivet stage die after formation of the final rivet stage closure part of FIG. 8;

FIG. 10, a view similar to FIG. 1 showing the upset rivet stage closure part for the securing of the tear strip tab thereon;

FIG. 11, a view similar to FIG. 2 showing the dies for forming the upset rivet stage closure part of FIG. 10;

FIG. 12, an enlarged fragmentary vertical sectional view showing the tab-secured closure part of FIG. 10 secured over the open end of a container;

FIG. 13, a top plan View of the closure and container of FIG. 12;

FIG. 14, an enlarged fragmentary vertical sectional view of the dies for forming the first stage bubble closure part of FIG. 1 with the dies in the fully closed position and the first stage bubble closure part of FIG. 1 therein;

FIG. 15, a view similar to FIG. 14, but of slightly reduced size, of the intermediate and second stage bubble dies with the first stage bubble closure part of FIG. 1 therein but prior to the complete operation of the intermediate stage thereof;

FIG. 16, a view similar to FIG. 15 but with the dies in position completing the formation of the intermediate stage bubble closure part of FIG. 3;

FIG. 17, a view similar to FIG. 16 but with the dies in position completing the formation of the second stage bubble part of FIG. 6;

FIG. 18, a view similar to FIG. 15 of the final rivet stage forming dies with the second stage bubble closure part of FIG. 6 therein and prior to the formation of the final rivet stage closure part;

FIG. 19, a view similar to FIG. 18 with the dies in position having completed the formation of the final rivet stage closure part of FIG. 8;

FIG. 20, a side elevation, with parts broken away and in vertical section, of the apparatus for automatically feeding the tear strip tab, positioning said ta'b over the final rivet of the final rivet stage closure part of FIG. 8, and performing the rivet upsetting operation, showing the final rivet stage closure part of FIG. 8 therein and prior to the operation of the apparatus;

FIG. 21, a view similar to FIG. 20 but taken at right angles to FIG. 20 and merely showing the upper rivet form die and the tab feed;

FIG. 22, a view similar to FIG. 21 with the upper rivet form die moved downwardly and having picked up a tab from the tab feed;

FIG. 23, a view similar to FIG. 20 with the upper rivet form die moved further downwardly and having positioned the tab over the final rivet of the final rivet stage closure part of FIG. 8; and

FIG. 24, a view similar to FIG. 23 with the final rivet upsetting operation of the dies complete for securing the tear strip tab to the closure wall portion.

Referring to FIGS. 1, 3, 6, 8, 10, 12 and 13, the various stage closure parts formed according to the principles of the present invention are shown, as well as the final metal closure secured to the open end of a container. The final closure construction, and the container and closure assembly shown and used herein for illustrating the methods of the present invention are disclosed and claimed in the co-pending application of George J. Henning et al., entitled Container Closure Construction, Ser. No. 333,812, filed Dec. 27, 1963, now abandoned.

As shown in FIG. 1, the first stage bubble closure part, generally indicated at 30, is preferably formed of strip metal stock, such as aluminum, and includes a disc-like wall portion 31 terminating outwardly in the usual inverted, generally U-shaped edge portion 32, with the upstanding, semi-spherical-like first stage bubble 33 formed, in this case, centrally thereof. Although in the particular final closure illustrated, it is desired to fasten the tear strip tab to the closure wall at this central location, it should be understood that such illustration is not meant to limit the method principles of the present invention, since such methods will be equally applicable to fastening locations in other areas of the closure wall, as long as such fastening is spaced sufficiently from the edge portion 32 so that the rivet forming operations may be accomplished.

The intermediate stage bubble part is shown generally at 34 in FIG. 3, and includes the wall portion 31 and edge portion 32 with the upstanding, semi-sphen'caI-like intermediate stage bubble 35. Bubble 35 is smaller in maximum diameter than the maximum diameter of the first stage bubble 33 of the first bubble stage part 30, and also of reduced height therefrom. Further, it will be noted that in this intermediate stage bubble part 34, the outer flange 36 of the edge portion 32 has been curled inwardly from that of the first stage bubble part 30, and this is for the dual purpose of preventing these parts from telescoping one over the other and sticking together when placed in stacks, and also, this somewhat aids in initiating the final formation of the closure edge portion during the securing of the closure to the walls of a container.

The second stage bubble part is shown generally at 37 in FIG. 6 and includes the wall portion 31, edge portion 32, and upstanding, semi-spherical-like second stage bubble 38 having still a smaller maximum diameter than the intermediate stage bubble 35 of the intermediate stage bubble part 34, but substantially the same height.

The final rivet stage part is shown generally at 33 in FIG. 8 and includes the wall portion 31, edge portion 32, and the upstanding, hollow, generally cylindrical final rivet 40 of a still smaller maximum diameter than maximum diameter of the second stage bubble 38 of the second stage bubble part 37, and of slightly less over-all height Furthermore, this final rivet stage part 39 may have the tab recess 41 formed in the wall portion 31 thereof, spaced from the final rivet 40, the over-all configuration of which may be seen more clearly in FIG. 13, and may also have the spaced tear strip score lines 42 formed therein, the over-all configuration of which is also best seen in FIG. 13. Still further, the rivet 40 is formed by the integral hollow, generally cylindrical side wall 43 and the integral transverse end wall 44, which end wall is, of course, spaced above the plane of the wall portion 31.

The upset rivet stage part 45 is shown generally in FIG. 10, and the only dilference between this part and the final rivet stage part 39 is that the tear strip tab 46 has been positioned flatwise against the wall portion 31 with the final rivet 40 received through a hole 47 of this tab. Furthermore, the rivet 40 has been upset so as to be provided with the rim portion 48 overlying the upper surface 49 of tab 46, thereby securing this tab to the closure wall portion 31.

Still further, the over-all height of the rivet 40 has been reduced to accomplish this upsetting operation. Finally, the tab 46 is positioned so as to extend from rivet 40 and overlie the tab recess 41 in the wall portion 31, with this tab preferably having a second hole 50 which may serve as an aid in gripping the end of the tab for accomplishing the ultimate tear strip tearing operation.

As shown in FIGS. 10, 12 and 13, these holes 47 and 50 formed in the tear strip tab 46 are formed symmetrical, as is the tab formed end-wise symmetrical, so that it is of no consequence which end of the tab is fastened to the closurewall portion 31 and which end overlies the tab recess 41. As will be discussed hereinafter, the purpose of this symmetrical formation of the tear strip tab 46 is for manufacturing convenience.

In FIGS. 12 and 13, the upset rivet stage part 45 is shown secured in usual manner to a container body, generally indicated at 51. Thus, in order to open the sealed container when it is desired, it is merely necessary to grasp the tear strip tab 46 around hole 50', as permitted by the recess 41, and pivot the tab upwardly, tilting the rivet 40 and causing the wall portion 31 to fracture along the tear strip score lines 42, after which, by continuing the tearing along the tear strip score lines, the entire wall portion 31 inwardly of the edge portion 32 may be removed.

The dies for forming the first stage bubble part 30 of FIG. 1 are illustrated in FIG. 14, with the portion thereof for forming the first stage bubble 33 of part 30 being shown enlarged in FIG. 2. Referring to FIGS. 2 and 14 the upper part of the dies include an upper punch holder 52, an upper form 53, an upper edge control form 54, an upper blank and edge form 55, a stock stripper 56, and an outer container ring 57, all assembled as shown.

It will be noted that the upper form 53 and blank and edge form 55 are secured to the upper punch holder 52 with the edge control form 54 contained vertically reciprocal therebetween. Furthermore, the stock stripper 56 is mounted vertically reciprocal by the O-rings 58 and is outwardly contained and limited by the outer container ring 57.

The lower part of the first stage bubble part dies include a die base 59, a lower form 60, a lower edge form 61, a lower knock-out ring 62 and a lower blank 63, all assembled as shown. It will be noted that the lower form 60, lower edge form 61 and lower blank 63 are secured to the die base 59, with the lower knock-out ring being mounted contained vertically reciprocal between the lower edge form 61 and lower blank 63, resiliently urged upwardly by the spring 64. Furthermore, the lower blank 63 is formed with a hardened insert 65 against which is performed the initial blanking of the stock, such stock being indicated by the broken lines 66.

For purposes of the methods of the present invention, the most important parts of the first stage bubble part dies of FIG. 14 are the generally cylindrical recess 67 of the upper form 53 having the ra-diused edge portion 68, and the upper semi-spherical-like surface 69 on the lower form 60. As shown in FIG. 14 and enlarged in FIG. 2, this upper form cylindrical recess 67 and lower form semi-spherical-like surface 69 cooperate to form the first stage bubble 33 of the first stage bubble part 30 shown in FIG. 1, as well as in FIGS. 2 and 14.

When the dies of FIG. 14 are in open position, the upper edge control form 54 and stock stripper 56 are at the downward limits of their reciprocal movement, and the lower knock-out ring 62 is resiliently urged to its upward limit by the spring 64. Furthermore, the metal stock 66 from which the part is to be formed overlies the lower part of the dies.

As the upper part of the dies of FIG. 14 moves downwardly, the upper edge control form 54, upper blank and edge form 55, and stock stripper 56 contact the stock 66 with the upper blank and edge form 55 blanking out the material for the first stage bubble part against the hardened insert 65 of the lower blank 63.

As the blank of metal stock is forced downwardly into the lower part of the dies by the upper blank and edge form 55, the upper edge control form 54 follows, whereas the stock stripper 56 is stopped against the upper surface 8 of the stock 66 overlying the hardened insert 65 of the lower blank 63.

Finally, the blank of metal stock contacts the lower edge form 61 with the upper blank and edge form 55 contacting lower knock-out ring 62, forcing this ring downwardly and bypassing the lower edge form 61 to form the fiange 36 on edge portion 32 of the first stage bubble part 30, as shown. At the same time, the upper edge control form 54 contacts the metal stock over the lower edge form 61 and this upper edge control form 54 moves upwardly to finally seat against the upper punch holder 52 and form the upper surface of the edge portion 32 of the first stage bubble part 30 over the lower edge form 61, as shown.

Most important to the method principles of the present invention, and still at the same time, the upper form 53 contacts the metal stock finally completing the formation of the edge portion 32 of the first bubble stage 30, but more important, forcing this metal stock downwardly against the upper semi-spherical-like surface 69 of lower form 60 by the radiused edge portion 68of the upper form cylindrical recess 67, thereby forming the primary or first stage bubble wall portion 33 of the first stage bubble part 30 with a spherically curved shape, as shown.

' The primary bubble wall portion 33 has a diameter at its concave open end, substantially larger than the diameter of the tab hole 47. During this formation of this first stage bubble 33, the metal stock of wall portion 31 is slightly drawn, stretched and thinned within the area of the first stage bubble 33, and also for an annular area of the wall portion 31 immediately outwardly adjacent the first stage bubble 33, that is, an annular area approximately 25% greater in outer diameter than the outer diameter of the first stage bubble 33.

As an example of the actual thinning of the metal stock,

in the area of the first stage bubble 33 during the formation of this first stage bubble, and taken from actual measurements of a series of parts made with the dies of FIG. 14, starting with an average metal thickness in the initial metal stock 66 of 0.0102 inch, the metal thickness in the area of the first stage bubble 33 after the formation of this bubble ranges from 0.009 inch to 0.0097 inch, depending on the location of the measurement. As can be seen, therefore, the metal in the area of the first stage bubble 33 is only slightly thinned during the formation of this bubble.

As the dies of FIG. 14 for the formation of the first stage bubble part 30 open, the stock stripper 56 strips the remaining stock 66 from the upper blank and edge form 55 while the upward urging of the lower knock-out ring 62 strips the first stage bubble part 30 from the lower edge form 61.

After the formation of the first stage bubble part 30 as described, this part passes through a conventional edge curling operation which forms the flange 36 of edge portion 32 inwardly, as shown in FIGS. 3 through 10. As previously stated, the purpose of this'edge curling operation is merely to form the edge portion 32 so that the parts will not telescope tightly one over the other and stick together when these parts are stacked, and also, such edge curling conveniently begins the formation of this edge portion 32 for finally securing the finished closure to a container body 51 (FIG. 12).

The two-stage dies for forming first, the intermediate stage bubble part 34 of FIG. 3, and then the second stage bubble part 37 of FIG. 6, both of which parts have been previously described, are shown in FIG. 15 in the initial operational position, and in FIGS. 16 and 17 in the progressive operational positions for forming the intermediate stage bubble part 34 and the second stage bubble part 37.

Referring first to FIG. 15, the upper part of the dies for forming the intermediate and second stage bubble parts 34 and 37 includes an upper part holder 70, a first form 71, a final form 72, an upper holder 73, and a die holder 74, all assembled as shown. It will be noted that the upper part holder 70 is mounted vertically reciprocal on the upper holder 73, being resiliently urged downwardly by the spring 75, the first form 71 is mounted vertically reciprocal within upper part holder 70 and around the final form 72, being resiliently urged downwardly by the spring 76, and the final form 72 is secured to the die holder 74.

The lower part of the dies of FIG. 15 for forming the intermediate and second stage bubble parts 34 and 37 include a bottom container 77, a pressure pad 78, and a two-piece lower form 79, all assembled as shown. It will be noted that the pressure pad 78 is mounted vertically reciprocal within bottom container 77 and surrounding lower form 79, with this pressure pad being resiliently urged upwardly by the spring 80.

Most important to the method principles of the present invention, the first form 71 is provided with the cylindrical recess 81 having the slightly radiused corner 82, and the final form 72 is provided with the cylindrical recess 83 having the slightly radiused corner 84. Furthermore, the lower fonn 79 is provided with the raised or upstanding semi-spherical-like forming surface 85.

As the upper part of the dies of FIG. 15 for forming the intermediate and second stage bubble parts 34 and 37 moves downwardly, the upper part holder 70 engages the first stage bubble part 30, forcing it downwardly against the pressure pad 78 and forcing this pressure pad to bottom downwardly against the lower form 79, in view of the fact that the upper part holder spring 75 is of considerably more strength than the pressure pad spring 80. This is the die position illustrated in FIGS. 4 and 15.

It will be noted that the upper part holder 70 grips the wall portion 31 of the first stage bubble part 30 downwardly against the pressure pad 78 and downwardly against lower form 79 directly outwardly and surrounding the first stage bubble 33. Thus, the metal of wall portion 31 is prevented from receiving any further working and thinning outwardly of the first stage bubble 33, so that the entire forming of the intermediate stage bubble 35 of the intermediate stage bubble part 34 must take place entirely from the metal contained in the first stage bubble 33.

Referring to FIGS. 5 and 16, the first form 71 has now moved downwardly within the upper part holder 70, contacted the first stage bubble 33 and forced this metal downwardly to form the smaller diameter and smaller height intermediate stage bubble 35. In this formation of the intermediate stage bubble 35, the edge extremities of the bubble are formed by the radiused corner 82 of the first form recess 83 while forcing the metal to assume asmaller diameter and smaller-height semi-spherical-like shape over and downwardly against the extreme upper portion of the pressure pad semi-spherical-like forming surface 85, all while the wall portion 31 of this part is being held or confined by the upper part holder 70 bearing downwardly against the pressure pad 78 and lower form 79.

During this formation of the intermediate stage bubble 35 to provide the intermediate stage bubble part 34, the metal thickness is again slightly reduced or thinned, that is, the metal of the first stage bubble 33 is slightly further drawn, stretched and thinned to form the smaller diameter intermediate stage bubble 35, and particularly in the location of this intermediate stage bubble. In view of the fact that this intermediate stage bubble 35 is formed by the two-stage die described, actual metal measurements have not been obtained at this particular intermediate point, that is, directly after the formation of the intermediate stage bubble 35 and before the formation of the second stage bubble 38.

Immediately after the formation of the intermediate stage bubble part 34, the final form 72 continues to move downwardly within the first form 71 and forms the secnd stage bubble 38 of the second stage bubble part 37, as shown in FIGS. 7 and 17. This second stage bubble 38 is formed over and relatively closely conforming to the semi-spherical-like forming surface of the pressure pad 78 by the radiused corner 85 of the final form recess 83, again further slightly drawing, stretching and thinning the metal, particularly in the area of the second stage bubble 38, and while the part wall portion 31 is being held or confined against further thinning immediately outwardly adjacent the intermediate stage bubble 35 by the first form 71.

Taking the measurements of the series of parts from the formation of the first stage bubble 33, as previously described, and thinning the metal thickness from the original average 0.0102 inch to the average range of 0.009 inch to 0.0097 inch in the formation of this first stage bubble 33, in the formation of the second stage bubble 38 from the first stage bubble 33 through the intermediate stage bubble 35, the metal is further thinned to the average range of 0.008 inch in the crown or upper portion of the second stage bubble 38, and 0.009 inch in the side portions of the second stage bubble 38, Thus, after the completion of the formation of the second stage bubble 38 of smaller diameter than the intermediate stage bubble 35, and still smaller diameter than the first stage bubble 33 by this series of progressively smaller diameter bubble formations, the metal finally making up the second stage bubble 38 has only been relatively slightly thinned from that of the original stock 66 (FIG. 14).

Although the foregoing double stage die operation is preferred for forming the first stage bubble 33 in two stages, that is, through the intermediate stage bubble 35, into the second stage bubble 38, in order to provide maximum control of the metal flow and to maintain a minimum of metal thinning for finally arriving at the second stage bubble 38, it is possible, with the use of metal stock which is relatively easily drawn and formed and/ or metal of different thickness, to form the second stage bubble 38 in a single stage die operation, directly from the first stage bubble 33. Furthermore, in the case of metal stock which is more diflicult to draw and form, and/ or of greater metal thickness, still additional bubble forming stages of similar type to those described may be added to maintain the metal thickness to the minimum desired, all clearly within the broad principles of the present invention.

The dies for forming the second stage bubble part 37 of FIG. 6 into the final rivet stage part 39 of FIG. 8 are shown in FIG. 18, with the upper part of these dies including the two-piece hold-down and form 86, the recess punch 87, the rivet form 88, and the upper container 89, all assembled as shown. It will be noted that the holddown and form 86 is mounted vertically reciprocal on the upper container 89, resiliently urged downwardly by the spring 90, while both the recess punch 87 and rivet form 88 are secured to the upper container 89.

The lower part of the dies for forming the final rivet stage part 39 include the lower container 91, the two-piece pressure pad and recess form 92, and the two-piece lower rivet form 93, all assembled as shown. Again, it will be noted that the pressure pad and recess form 92 is mounted reciprocal within the lower container 91 and outwardly surrounding the lower rivet form 93, being upwardly contained by the lower container 91 and resiliently urged upwardly by the spring 94, with both the lower container 91 and lower rivet form 93 being mounted stationary.

More important to the method principles of the present invention, the rivet form 88 is formed with a cylindrical recess 95 having the radiused corner 96, and the lower rivet form 93 is provided with the generally cylindrical rivet-like surface 97 substantially conforming to the interior of the final rivet 40. Furthermore, but rather of conventional construction, is the lower arcuate surface 98 on the recess punch 87 and the recess 99 in the upper surface of the pressure pad and recess form 92.

As the upper part of the dies of FIG. 18 for forming the final rivet stage part 39 moves downwardly, the holddown and form 86 first engages the wall portion 31 of the second stage bubble part 37, gripping this wall portion against the pressure pad and recess form 92, and this gripping of wall portion 31 is at substantially the same diameter as the outer diameter of the first stage bubble 33 of the first stage bubble part 30. Immediately thereafter, the lower surface 98 of recess punch 87 begins to engage the wall portion 31 and, more important, the radiused corner 96 of the rivet form recess 95 begins to engage the top surface of the second stage bubble 38, which is the position of the dies shown in FIG. 18.

As shown in FIGS. 9 and .19, the further and final downward movement of the upper part of the dies for forming this final rivet stage part 39 causes the recess punch 87 to complete the formation of the tab recess 41 downwardly within the recess 99 of the pressure pad and recess form 92, while the rivet form recess 95 and the radiused corner 96 thereof completes the formation of the final rivet 40 over the rivet-like surface 97 of the lower rivet form 93.

Thus, the final rivet blank 40 is formed of still smaller diameter than the maximum diameter of the second stage bubble 38 and of less height, so as to have a cup shape formed by the upstanding hollow cylindrical side wall 43 and transverse end wall 44 spaced above the wall portion 31 of the final rivet. stage part 39. Furthermore, during the formation of the final rivet 40 from the second stage bubble 38, the metal of this second stage bubble is merely formed downwardly into the final rivet 40 without any appreciable change in metal thickness, so that no further thinning of the metal is required for the formation of the final rivet, but rather this operation consists only of repositioning, relocating or reshaping the metal of the second stage bubble 38 for forming the final rivet 40.

Again, by actual measurements of the series of parts, it was found that, as before stated, the metal thickness in the second stage bubble 38 in the top or crown area was 0.008 inch and in the side portions was 0.009 inch, and in this final rivet 40, the metal thickness of the end Wall 44 is 0.008 inch and in the side wall 43 is 0.009

inch. This, therefore, indicates the mere repositioning of the metal without thinning the second stage bubble 38 to form the final rivet 40.

If embossing of directions and other printed material in the wall portion 31 of the final closure part is desired, this may be accomplished during the forming of this final rivet stage part 39 in the dies of FIG. 18, merely by providing the necessary embossing configurations in the hold-down and form 86 and pressure pad and recess form 92 in the conventional manner. Furthermore, the forming of the final rivet stage part 39, and prior to the formation of the assembled upset rivet stage part 45, conventional spaced tear. strip score lines 42 may be formed around final rivet 40 and along the closure wall portion 31, as desired, and in the conventional manner, for instance, in the pattern shown in the finished closure part of FIG. 13.

The final assembly apparatus including the tab feed and rivet upset dies for forming the upset rivet stage part 45 of FIG. 10, are shown in FIGS. 20 and 21, with the upper part of the dies including the vacuum holder and pressure pad 100, the tab pilot 101, the rivet upsetting quill 102, and the container 103, all assembled as shown. It will be noted that the vacuum holder and pressure pad 100 is mounted vertically reciprocal on the container 103, resiliently urged downwardly by the spring 104, the tab pilot 101 is mounted vertically reciprocal in the vacuum holder and pressure pad 100, resiliently urged downwardly by the spring 105, and the vacuum holder and pressure pad 100 is mounted vertically reciprocal over the rivet upsetting quill 102, with this quill being secured to the container 103. Furthermore, a vacuum channel 106 is formed through a portion of the vacuum holder and pressure pad 100 opening downwardly substantially centrally thereof and to which a vacuum line, for the sake of simplicity not shown, may

be connected for a purpose to be hereinafter described.

The lower part of the rivet upsetting dies includes an outer container ring 107, a pressure pad 108, a rivet back-up holder 109, a rivet upsetting pilot 110, and a diebase 111, all assembled as shown. It will be noted that the outer container ring 107 and rivet back-up holder 109 are secured to the die base 111, with the pressure pad 108 being vertically reciprocally mounted therebetween and resiliently urged upwardly by the spring 112, while being upwardly contained by the outer container ring 107. It will be further noted, and most important to the principles of the present invention, that the rivet upsetting pilot 110 which is secured recessed in the rivet back-up holder 109 is formed with an upstanding rivet pilot mem- 1 her 113 which substantially conforms in size to the inner diameter ofthe side wall 43 of the final rivet 40 on thefinal rivet stage part 39, but with this rivet pilot member 113 having a marked less vertical dimension than the internal vertical dimensions of the final rivet side wall 43. The importance of this dimensioning of the rivet pilot member 113 relative to the internal dimensions of the final rivet 40 will be hereinafter discussed more in detail.

The tab feed mechanism includes a mounting block 114 secured to the die base 111 and in turn mounting the tab holder container 115 spaced above the lower part of the rivet upsetting dies and spaced below the upper part of these rivet upsetting dies. Furthermore, this tab feed mechanism includes the tab stop 116, the opposed tab grip fingers 117, the finger mounting blocks 118, the finger mounting top plate 119,the tab feed track 120,

and the tab pusher mechanism 121, all assembled as shown.

As best seen in FIG. 20, the tab stop 116 is secured to the tab holder container 115 aligned with the channellike tab feed track 120, with the tab stop 116 being positioned at one side of the tab grip fingers 117 and the tab feed track 120 terminating at the other side. Furthermore, the tab pusher mechanism 121 is mounted mechanically horizontally reciprocal in the direction of the tab grip fingers 117 along the tab feed track 120, such reciprocations being accomplished in the usual manner and being timed in the usual manner for one reciprocation prior toeach downward stroke of the upper part of the rivet upsetting dies. As shown, a pivotal push rod 122 is resiliently urged upwardly to engage in the rivet hole 47 of each successive tab 46 for the successive adcontainer 115. Also, the tab grip fingers 117 are urged pivotally toward one another by the spring loaded pins 123 bearing thereagainst, and this inward pivotal movement of the tab grip fingers 117 is limited by the stop screws 124, as shown.

-Thus these tab grip fingers 117 are resiliently urged toward each other by the spring loaded pins 123, but are limited in this inward pivotal movement by the stop screws 124, so that the tab receiving slots 125 of these grip fingers remains spaced apart the exact proper distance and aligned with the tab feed track 120 for re ceiving the edges of one of the tabs 46 in these tab receiving slots 125, and retaining such tab underlying the lower surface'130 of the vacuum holder and pressure pad 100 of the rivet upsetting die upper part. Furthermore, due to the resilient mounting of the pins 123, these tab grip fingers 117 may spread apart a limited distance when so urged, so as to release a particular tab 46 from the tab receiving slots 125 thereof, as will be hereinafter described.

As shown in FIG. 20, at the beginning of the operation for forming the tab assembled upset rivet stage part 45 from the final rivet stage part 39, one of the tabs 46 has been fed by the tab feed track 120 and tab pusher mechanism 121 to a position gripped in the tab receiving slots 125 of the tab grip fingers 117, properly positioned directly underlying the lower surface 130 of the vacuum holder and pressure pad 101 of the upper die part. Furthermore, the tab pilot 101 of this upper die part is resiliently urged downwardly projecting below the lower surface 130 of the vacuum holder and pressure pad 100, while the fiat end surface 126 of the rivet upsetting quill 102 is recessed upwardly within the cylindrical quill opening 127 of the vacuum holder and pressure pad 100, due to the downward resilient urging of this pressure pad. Still further, the final rivet stage part 39 upon which the tab assembly and rivet upsetting operation is to be performed is positioned over the pressure pad 108 of the lower part of the dies, spaced above the rivet upsetting pilot 110, due to the resilient upward urging of the pressure pad 108.

As shown in FIG. 21, the upper part of the dies has begun to move downwardly toward the tab holder assembly, and in FIG. 22, the vacuum holder and pressure pad 100 has telescoped through this tab feed assembly between the tab grip fingers 117. During this telescoping, the cam surface 128 of the vaccum holder and pressure pad 100 engages the opposed cam surfaces 129 of the tab grip fingers 117 at the exact moment that the lower surface 130 of the vacuum holder and pressure pad 100 engages the particular tab 46.

This cam surface engagement and continued downward movement of the vacuum holder and pressure pad 100 spreads the tab grip fingers 117 against the resilient urging of the pins 123, thereby releasing the tab 46 held between these fingers, and at the same time, the downwardly projecting tab pilot 101 enters the hole 50 of the tab 46, while vacuum is initiated in the vacuum channel 106 of the vacuum holder and pressure pad 100. This vacuum holds the tab 46 against the lower surface 130 of the vacuum holder and pressure pad 100 for the further downward movement free of the tab grip fingers 117, and the tab pilot 101 maintains this tab exactly properly positioned by extending through the tab hole 50, as shown in FIG. 22.

Also, as will be more apparent from FIGS. 11, 23 and 24, when the tab 46 is positioned in the tab grip fingers 117 ready for pick up by the lower surface 130 of the vacuum holder and pressure pad 100, the other tab hole 47 which is to ultimately be telescoped over and receive the final rivet 40 of the final rivet stage part 39 therethrough, is exactly vertically aligned with and above this final rivet 40, and is also exactly vertically aligned with and below quill opening 127 of the vacuum holder and pressure pad 100. Thus, when the tab 46 is engaged by the lower surface 130 of the vacuum holder and pressure pad 100, not only will the tab hole 50 receive the downwardly projecting tab pilot 101 therethrough, but the tab hole 47 will be positioned exactly co-axial with the quill opening 127 at the lower surface 130 of the vacuum holder and pressure pad 100.

Due to the fact that the tabs 46 are formed symmetrical and the tab holes 47 and 50 are positioned symmetrically in either end of the tabs, as previously discussed, it is immaterial which end of any particular tab 46 is fed first into the tab receiving slots 125 of the tab grip fingers 117, since in final position between the tab grip fingers 117, one of these tab holes will always be in proper vertical alignment with the tab pilot 101 of the vacuum holder and pressure pad 100, and the other tab hole will always be in proper vertical alignment with both the quill opening 127 of the vacuum holder and pressure pad 100 and the final rivet 40 of the final rivet stage part 39, as previously described.

As shown in FIG. 23, the vacuum holder and pressure pad finally moves downwardly to position the particular tab 46 fiatwise over the wall portion 31 of the final rivet stage part 39, with the final rivet 40 extending upwardly through the tab hole 47, and the tab 46 extending partially overlying and the hole 50 thereof partially overlying the tab recess 41 in wall portion 31. At the same time, the final rivet 40 of the final rivet stage part 39 is received upwardly into the quill opening 127 of the vacuum holder and pressure pad 100, with the rivet side wall 43 spaced inwardly from the side walls of the quill opening 127 and with the rivet end wall 44 spaced downwardly from the fiat end surface 126 of the rivet upsetting quill 102.

This downward pressure against the final rivet stage part 39 resulting from the downward movement of the tab 46 by the vacuum holder and pressure pad 100 causes a partial retraction of the tab pilot 101, as shown in FIG. 23, and also forces the pressure pad 108 of the lower part of the dies to move vertically downwardly bottoming on the rivet back-up holder 109. This results in the final rivet 40 of the final rivet stage part 39 telescoping downwardly over the rivet pilot member 113 of the rivet upsetting pilot 110, again as shown in FIG. 23.

At this stage, the tab 46 is properly positioned over the final rivet 40 of the final rivet stage part 39 and lying fiatwise over the wall portion 31 of this part, while the final rivet 40 is supported from beneath along the lower portion of the side walls 43 by the rivet pilot member 113, but spaced downwardly from the end wall 44 of this final rivet, and this particular degree of inward supporting of the final rivet 40 is of importance to the principles of the present invention. In other words, the final rivet side wall 43 is supported against inward collapse at the lower portion of this side wall, inwardly adjacent the tab 46, but the upper portion of this final rivet side wall 43 is not internally supported, nor is the final rivet end wall 44 internally supported.

Finally, as shown in FIG. 24, after the final positioning of the tab 46 over the final rivet 40 and the positioning of the rivet pilot member 113 supporting this final rivet, continued downward movement of the container 103 of the upper part of the dies forces this container against the vacuum holder and pressure pad 100, and at the same time, moves the rivet upsetting quill 102 downwardly relative to the vacuum holder and pressure pad 100 and within the quill opening 127. As this rivet upsetting quill 102 moves downwardly in the quill opening 127, the quill fiat end surface 126 engages the end wall 44 and axially presses the side and end walls of the final rivet 40, displacing this rivet end wall fiatwise downwardly, and displacing and upset folding the upper part of the rivet side wall 43 in the region where the side wall 43 joins the end wall 44 outwardly to the positions shown in FIGS. 10 and 11, forming the rivet outwardly extending rim portion 48 engaging and overlying the upper surface 49 of tab 46 around the tab hole 47, thereby securing the tab to the closure wall portion 31 and forming the completed upset rivet stage closure part 45 of FIGS. 10 and 11. As stated, and as shown in FIG. 23, the support of the rivet side wall 43 during this rivet upsetting operation by the rivet pilot member 113 on the lower part of the dies is only at the lower portion of this side wall 43, extending inwardly adjacent the tab 46 and only slightly above the tab upper surface 49, but still spaced downwardly a considerable distance from the rivet end wall 44. This support of the lower portion of the rivet side wall 43 prevents the side wall collapsing inwardly and this is the sole purpose of such support.

Furthermore after the upsetting of the final rivet 40, as shown in FIG. 24 and in enlarged fragmentary view in FIG. 11, the rivet end wall 44 is still spaced above this internal support of the rivet pilot member 113, so that during this upsetting operation, the rivet end wall 44 can only be displaced downwardly and absolutely no impact force which would result in thinning of the rivet end wall 44 can take place. Obviously, if it were desired, the internal support by the rivet pilot member 113 could be constructed such that at the completion of this upsetting operation, the rivet end wall 44 would just touch this rivet pilot member 113 and the same thing would be accomplished, but it is important that no impact force be exerted by the rivet upsetting quill 102 against this rivet end wall 44 which could cause thinning of the metal therein.

Still further, it is desirable that the quill opening 127 of the vacuum holder and pressure pad 10a within which the final rivet 40 is received and the upsetting operation takes place, be of sufficient diameter so that when the rivet upsetting operation is complete, the rivet rim portion 48 will not contact or at least only lightly contact the vacuum holder and pressure pad 100 within this quill opening 127. This spacing of the rivet rim portion 48 or the mere light contact thereof will insure that the upset rivet will not stick in this quill opening 127 and cause problems of removal.

Thus, in this final rivet upsetting operation, the rivet end wall 44 is merely displaced or relocated downwardly, and the rivet side wall 43 displaced or relocated downwardly and folded outwardly, without metal thinning of the final rivet 40. Again, from actual measurements taken from the series of closure parts, it is found that the upset rivet end wall still has a metal thickness of 0.008 inch providing an extremely strong rivet for resisting the forces exerted when the tab 46 is used to manipulate the tear strip formed by tear strip score lines 42.

This upset rivet stage part 45,,as shown in FIG. 10, is, therefore, now complete and ready for fastening to a container body 51 in the usual manner, the completed container-closure assembly being shown in FIGS. 12 and 13.

Thus, according to the method principles of the present invention, a tear strip tab 46 is fastened to the central wall portion 31 of the container closure by forming a series of integral progressively smaller upstanding semispherical-like bubbles 33, and 38 in this centralswall portion, while progressively slightly thinning the metal of this wall portion. In the formation of the first bubble 33, the metal is thinned slightly in the area of the bubble, and also slightly outwardly thereof in an annular area around bubble 33 of a maximum diameter approximately twenty-five percent greater than the maximum diameter of bubble 33. The intermediate stage bubble 35, is formed, and the final or second stage bubble 38 are formed entirely of the metal in the first stage bubble 33, while progressively slightly thinning this metal, and preferably while holding the metal of the wall portion 31 directly outwardly of the first stage bubble 33 to form the intermediate stage bubble 35, and holding the metal directly outwardly of the intermediate stage bubble 35 to form the second stage bubble 38.

Thereafter, the second stage bubble 38 is formed into an upstanding rivet-like member or rivet 40 having the hollow generally cylindrical side wall 43 and a transversely extending end wall 44 spaced above the central wall portion 31, with this rivet 40 being formed from the bubble 38 of less maximum diameter and less height than the bubble 38, merely by relocating or repositioning the metal of bubble 38 and without further thinning of the metal. Then, in the final tab assembly operation, the tab 46, having the opening 47, may be automatically fed to a location vertically above the final rivet 40 with the tab properly oriented to the closure wall portion 31 and the tab hole 47 vertically aligned with the final rivet 40, the tab 46 moved vertically downwardly flatwise against the closure wall portion 31 with the rivet 40 received upwardly through the tab hole 47 and extending above the tab upper surface 49, and the rivet 40 upset to form the rivet rim portion 48 overlying the tab 46 around the tab hole 47, to thereby secure the tab to the closure wall portion 31.

During this rivet upsetting operation, the rivet end wall 44- is merely relocated fiatwise downwardly without impact force, and the upper portion of the rivet side wall 43 is relocated or repositioned downwardly and folded outwardly, to form the rivet rim portion 48 overlying the wall portion 31, and without metal thinning. Also during this rivet upsetting operation, the lower portion of the rivet side wall is inwardly supported, both inwardly of the tab 46 and downwardly thereof, against inward collapse.

The final upset rivet formed according to the principles of the present invention, therefore, provides a final upset rivet having metal wall thicknesses throughout only slightly thinned from the original wall thickness of the closure wall portion 31 from which this upset rivet is formed, and free from any radically thinned areas which would weaken the over-all upset rivet construction. This, thereby, provides an extremely strong fastening means between the tab 46 and closure wall portion 31 which will withstand the necessary relatively high forces required for the manipulation of a tear strip formed in the closure wall portion 31.

In the foregoing description, certain terms have been used for brevity, clearness and understanding but no unnecessary limitations are to be implied therefrom, because such wo-rds are used for descriptive purposes herein and are intended to be broadly construed.

Moreover, the embodiments of the improved methods, procedures and steps illustrated and described herein are by way of example and the scope of the present method inventions are not limited to the exact details shown.

Having now. described the invention, the preferred methods, procedures and steps thereof, and the advantageous new and useful results obtained thereby, the new and useful methods and reasonable equivalents thereof obvious to those skilled in the art are set forth in the appended claims.

We claim:

1. In a method of fastening a tab to a central portion of a metallic container wall wherein the tab is formed with a hole telescoped over a cup-shaped rivet blank projecting integrally from said container wall and the rivet blank is formed with a rim overlying the tab surface around the hole, the steps of:

forming in a sheet metal wall blank a primary bubble wall portion having a spherically curved shape of predetermined height and a concave open end diameter substantially larger than the diameter of said tab hole while slightly reducing the thickness of the blank over a limited annular area adjacent said primary bubble; drawing, stretching and thinning the metal in said primary bubble wall portion during formation thereof; then while confining the blank metal around the primary bubble wall open end, drawing and stretching the metal in the primary bubble wall portion to form a secondary bubble wall portion having a spherically curved shape and an open end of smaller diameter than that of the primary bubble wall portion and having a height reduced from that of the primary bubble wallportion while slightly thinning the metal in the secondary bubble wall portion during said drawing and stretching;

repositioning and reshaping the metal in the secondary bubble wall portion to form a cup-shaped rivet blank having a cylindrical side wall and an end wall defining a rivet blank height slightly less than the height of the secondary bubble wall portion and a cup side wall of smaller diameter than the secondary bubble open end diameter while maintaining the cup end wall metal thickness the same as the thickness of the secondary bubble wall portion during formation of the rivet blank;

telescoping the tab hole over said cup-shaped rivet blank;

and axially pressing the rivet blank end and side walls and upset folding said side wall outwardly downwardly in the region where said side wall joins the rivet blank end wall to reduce the rivet blank height and to form a rim overlying the tab around the tab hole while internally supporting the cylindrical side wall of the rivet blank and while maintaining said internal support free of rivet blank end wall contact to maintain the end wall thickness of the upset rivet blank the same as the thickness of the rivet blank and wall before upsetting.

2. In the method set forth in claim 1 the further step of forming the secondary bubble wall portion entirely from metal in the primary bubble wall portion.

3. In the method set forth in claim 1 the step of reshaping of the primary bubble wall portion to form a secondary bubble wall portion in two stages, comprising:

drawing and stretching the metal in the primary bubble wall portion to form an intermediate bubble wall having an open end of smaller diameter than that of the primary bubble wall portion and having a height reduced from that of the primary bubble wall portion, while meanwhile confining the blank metal around the primary bubble wall open end, and while slightly thinning the metal in the intermediate bubble wall portion during the formation of the intermediate bubble wall;

then while confining the blank metal around the intermediate bubble wall open end, drawing, stretching and thinning the metal in the intermediate bubble wall to form the secondary bubble wall having an 18 open end of smaller diameter than that of the intermediate bubble wall and having a height substantially the same as that of the intermediate bubble wall.

4. In the method set forth in claim 3 the further steps of forming the intermediate bubble wall entirely from metal in the primary bubble wall portion, and forming the secondary bubble wall portion entirely from metal in the primary bubble wall portion.

5. The method set forth in claim 1 in which the thinning of the metal from sheet metal wall blank original thickness to cup end wall thickness of the riveted rivet blank is controlled such that with sheet Wall blank metal 0.0102" thick the primary bubble wall portion thickness is from 0.009 to 0.0097" thick, the crown of the secondary bubble wall portion is 0.008" thick, the end wall of the cup-shaped rivet blank is 0.008" thick, and the end wall of the upset and folded rivet is 0.008" thick.

References Cited UNITED STATES PATENTS 1,715,812 6/1929 Bauer. 1,870,728 8/1932 Hothersall. 3,151,766 10/1964 Henchert. 3,191,564 6/1965 Fraze 29509 X 3,196,817 7/1965 Fraze 29430 X FOREIGN PATENTS 590,720 6/1947 Great Britain. 661,638 11/1951 Great Britain.

CHARLIE T. MOON, Primary Examiner. 

1. IN A METHOD OF FASTENING A TAB TO A CENTRAL PORTION OF A METALLIC CONTAINER WALL WHEREIN THE TAB IS FORMED WITH A HOLE TELESCOPED OVER A CUP-SHAPED RIVET BLANK PROJECTING INTEGRALLY FROM SAID CONTAINER WALL AND THE RIVET BLANK IS FORMED WITH A RIM OVERLYING THE TAB SURFACE AROUND THE HOLE, THE STEPS OF: FORMING IN A SHEET METAL WALL BLANK A PRIMARY BUBBLE WALL PORTION HAVING A SPHERICALLY CURVED SHAPE OF PREDETERMINED HEIGHT AND A CONCAVE OPEN END DIAMETER SUBSTANTIALLY LARGER THAN THE DIAMETER OF SAID TAB HOLE WHILE SLIGHTLY REDUCING THE THICKNESS OF THE BLANK OVER A LIMITED ANNULAR AREA ADJACENT SAID PRIMARY BUBBLE; DRAWING, STRETCHING AND THINNING THE METAL IN SAID PRIMARY BUBBLE WALL PORTION DURING FORMATION THEREOF; THEN WHILE CONFINING THE BLANK METAL AROUND THE PRIMARY BUBBLE WALL OPEN END, DRAWING AND STRETCHING THE METAL IN THE PRIMARY BUBBLE WALL PORTION TO FORM A SECONDARY BUBBLE WALL PORTION HAVING A SPHERICALLY CURVED SHAPED AND AN OPEN END OF SMALLER DIAMETER THAN THAT OF THE BUBBLE WALL PORTION AND HAVING A HEIGHT REDUCED FROM THAT OF THE PRIMARY BUBBLE WALL PORTION WHILE SLIGHTLY THINNING THE METAL IN THE SECONDARY BUBBLE WALL PORTION DURING SAID DRAWING AND STRETCHING; REPOSITIONING AND RESHAPING THE METAL IN THE SECONDARY BUBBLE WALL PORTION TO FORM A CUP-SHAPED RIVET BLANK HAVING A CYLINDRICAL SIDE WALL AND AN END WALL DEFINING A RIVET BLANK HEIGHT SLIGHTLY LESS THAN THE HEIGHT OF THE SECONDARY BUBBLE WALL PORTION AND A CUP SIDE WALL OF SMALLER DIAMETER THAN THE SECONDARY BUBBLE OPEN END DIAMETER WHILE MAINTAINING THE CUP END WALL METAL THICKNESS THE SAME AS THE THICKNESS OF THE SECONDARY BUBBLE WALL PORTION DURING FORMATION OF THE RIVET BLANK; TELESCOPING THE TAB HOLE OVER SAID SUP-SHAPED RIVET BLANK; AND AXIALLY PRESSING THE RIVET BLANK END AND SIDE WALLS AND UPSET FOLDING SAID SIDE WALL OUTWARDLY DOWNWARDLY IN THE REGION WHERE SAID SIDE WALL JOINS THE RIVET BLANK END WALL TO REDUCE THE RIVET BLANK HEIGHT AND TO FORM A RIM OVERLYING THE TAB AROUND THE TAB HOLE WHILE INTERNALLY SUPPORTING THE CYLINDRICAL SIDE WALL OF THE RIVET BLANK AND WHILE MAINTAINING SAID INTERNAL SUPPORTING FREE OF RIVET BLANK END WALL CONTACT TO MAINTAIN THE END WALL THICKNESS OF THE UPSET RIVET BLANK THE SAME AS THE THICKNESS OF THE RIVET BLANK AND WALL BEFORE UPSETTING. 